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BIOCHEMICAL INVESTIGATIONS IN THE DIAGNOSTICS OF CARDIOVASCULAR DISORDERS. As. MARUSHCHAK M.I. Heart attack symptoms. Acute MI. Measurement of cardiac enzyme levels.
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BIOCHEMICAL INVESTIGATIONS IN THE DIAGNOSTICS OF CARDIOVASCULAR DISORDERS As. MARUSHCHAK M.I.
Measurement of cardiac enzyme levels • Measure cardiac enzyme levels at regular intervals, starting on admission and continuing until the peak is reached or until 3 sets of results are negative. Biochemical biomarkers are useful for both diagnosis and prognostication
This plot shows changes in cardiac markers over time after the onset of symptoms. Peak A is the early release of myoglobin or creatine kinase isoenzyme MB (CK-MB) after acute myocardial infarction (AMI). Peak B is the cardiac troponin level after infarction. Peak C is the CK-MB level after infarction. Peak D is the cardiac troponin level after unstable angina. Data are plotted on a relative scale, where 1.0 is set at the myocardial-infarction cutoff concentration. Courtesy of Wu et al (1999). ROC = receiver operating characteristic.
Measurement of CK-MB levels • CK-MB, the isoenzyme specific to the heart muscle, was the principal biomarker of cardiac injury until troponin supplemented it. • In the setting of myocardial infarction, plasma CK-MB concentrations typically rise about 4-6 hours after the onset of chest pain. They peak within 12-24 hours and return to baseline levels within 24-48 hours. • Serial measurements obtained every 6-8 hours (at least 3 times) are warranted until peak values are determined.
Clinical settings other than acute coronary syndrome, such as trauma, heavy exertion, and skeletal muscle disease (eg, rhabdomyolysis) may elevate CK-MB values. • The area under the concentration-time curve for CK-MB created with serial measurements of blood enzyme levels provides a reliable estimate of the size of the infarct. • Determination of subforms of CK-MB (CK-MB2 that is more specific to heart muscle) may improve the sensitivity of this test.
Measurement of troponin levels • Troponin is part of the contractile apparatus of the myocyte associated with tropomyosin and actin and myosin filaments. Troponin has 3 subunits: TnT, TnI, and TnC. TnI and TnT are normally not detectable in the blood. • Measurement of troponin level has both diagnostic and prognostic value. • Positive troponin levels are virtually diagnostic of myocardial infarction in the most recent revisions of the ACC/AHA guidelines, as they are without equal in terms of combined specificity and sensitivity in diagnosing myocardial infarction. • Elevated troponin levels might help in identifying patients who might greatly benefit from aggressive antiplatelet and other adjunctive therapy. • Troponin levels are typically measured serially along with CK values.
Measurement of myoglobin levels • Myoglobin is not cardiac specific, but it may be detected as early as 2 hours after myocardial necrosis starts. • Myoglobin results should be supplemented with other more specific cardiac biomarkers, such as CK-MB or troponin. • Myoglobin values have a high negative predictive value when blood is sampled in the first 4-8 hours after onset.
Lactate dehydrogenase • Enzyme isoforms • LDH-1 (4H) - in the heart • LDH-2 (3H1M) - in the reticuloendothelial system • LDH-3 (2H2M) - in the lungs • LDH-4 (1H3M) - in the kidneys • LDH-5 (4M) - in the liver and striated muscle
Histologic section of the myocardium showing a cross-section of coronary artery affected by atherosclerosis and myocyte hypertrophy
Histologic section of an autopsy myocardial specimen from a patient with long-standing hypertension and associated coronary artery disease. The slide shows myocardial hypertrophy, contraction bands (typical of left ventricular hypertrophy), and "car box" nuclei.